ZOL 355 Lecture 17 Outline of Last Lecture I Atmospheric CO2 and the Carbon cycle II The Ocean sink III Biological cycle IV Geological cycle V Carbon Isotopes Outline of Current Lecture I II III IV V VI Photosynthesis CO2 fixation Water loss issues C4 vs C3 plants Challenges with water temperature Challenges with water buoyancy Current Lecture I II III IV water stress photosynthesis photosynthesis in plants C3 photo a cellular arrangement i stomata opening for gas exchange ii bundle sheath cells no chloroplasts CO2 fixation initial step a CO2 reacts with RuBP to for 3PG b requires an enzyme i RuBP C c part of Calvin Benson cycle occurs in mesophyll cells d requires high CO2 e can react with CO2 or O2 f greater tendency to react with O2 than CO2 high affinity for O2 Issue for water loss a stomata close to prevent water loss b CO2 falls reduces likelihood of photo c photorespiration dominates V VI VII VIII IX X XI XII XIII XIV XV XVI XVII XVIII C4 a bundle sheath cells with chloroplasts mesophyll cell b CO2 comes from OAA formed from atmospheric CO2 all occurs in mesophyll cells it has compartmentalized the Calvin Benson in the bundle sheath with the initial step of CO2 fixation occurring the bundle sheath cell c fixation of CO2 results in formation of a 4C compound d CO2 reacts with PEP to form 4C compound OAA e CO2 PEP OAA f requires an enzyme PEP C g Takes place in mesophyll cell but in C4 plants sugars are not made in mesophyll cell Maintaining high CO2 near RuBP C a OAA diffuses from mesophyll cell into bundle sheath cells b OAA breaks down to CO2 pyruvate in bundle sheath cell c C4 have very efficient production of CO2 RuBP C will not be limited by CO2 d CO2 RuBP 3PG usesRuBP C e production of 3PG occurs in bundle sheath cells f bundle sheath cells are not near surface of leaf so O2 concentration also reduced Advantage of C4 plants a have PEP C which does not react with oxygen fixes CO2 at low concentration so stomata can close more to reduce water loss and it keeps CO2 concentration high for RuBP C C3 vs C4 CBC used both CBC occurs in mesophyll cells C3 occurs in bundle sheath in C4 down farther away from dermis so O2 isn t an issue for RuBP C CO2 fixing enzyme associated with first step RuBP C takes CO2 sticks in onto RuBp in C3 PEP C for C4 Photorespiration C3 extensive C4 minimal First product of CO2 fixation C3 3PG C4 OAA Cells involved in photosynthesis C3 mesophyll only C4 mesophyll and bundle sheath Is 3PG made in C4 yes Physiological Ecology Part 2 Challenges in water temperature a water freezes b liquid over a wide temp range c changes temp and state slowly d freshwater densest at 4C Challenges in water buoyancy a organisms are more dense so they have to compensate for sinking b stingray has large pectoral fins which provides lift for example c viscous drag influences buoyancy friction between the organism and water the more friction viscous drag the less you sink XIX XX XXI i In order to create more drag create more surface area belly flop vs dive d it is influenced by SA V i organism with a large SA V reduces tendency to sink ii small cells have a high SA area relative to V iii small cells sink slower Phytoplankton can alter their viscous drag It has spines that can break off to allow it to sink oil gas bulbs and swim bladders increase buoyancy adaptation to maintain water balance a marine fish maintain osmotic potential via salt production i body of fish has lower salt concentration than ocean fish is hypo osmotic relative to ocean ii water moves out of fish to ocean iii replace water by drinking seawater iv marine fish cells hypo ostomotic salt concentration is low v ocean water hyper osmotic high salt concentration